The present invention generally relates to microelectromechanical devices and in particular to a microelectromechanical apparatus having a platform which can be elevated and tilted, for example, to form a micromirror for redirecting or switching an incident light beam. The present invention has applications for forming an array of tiltable micromirrors for use in switching light beams between a plurality of input optical fibers and a plurality of output optical fibers, or for forming a projected light display.
The use of fiber optics for data communications and telecommunications is desirable to increase the bandwidth for information transmission. Lasers used for fiber optics communications produce light that can be modulated at rates up to many tens of Gigahertz (GHz). Multiple laser beams can also be wavelength division multiplexed for transmission through a single optical fiber. Presently, a limitation in information transmission with fiber optics is in routing of optical signals (i.e. modulated light) between different fibers. Thus, the need exists for optical switching technology to redirect the optical signals or portions thereof from one optical fiber to any of up to hundreds or more other optical fibers.
Surface micromachining, which can be used to build-up microelectromechanical systems (MEMS) layer by layer, is a promising technology for forming such optical signal routers (i.e. switches). The present invention is directed to a platform supported by two or three compliant elevation structures so that the platform can be tilted in an arbitrary direction to form in combination with an optical coating disposed thereon an optical switch which can be used for fiber optics signal routing, or for redirecting incident light beams for other applications such as projection displays.
An advantage of the present invention is that control of the tilt angle of the platform can be achieved by independently controlling one or more compliant elevation structures, thereby providing precise angular positioning of the platform over large tilt angles (e.g. xc2x120 degrees).
Another advantage of the present invention is that the use of compliant elevation structures to elevate and/or tilt the platform eliminates rubbing surfaces and thereby decreases or prevents wear-induced changes in performance over time.
A further advantage of the present invention is that the platform can be elevated or tilted with negligible stress or deformation of the platform induced by the compliant elevation structures.
Yet another advantage of the present invention is that the platform can be elevated without tilting by operating a plurality of the compliant elevation structures in unison. Such an elevatable platform can be used, for example, to control the focal plane of a focusing lens within an optical data storage device to within a fraction of a micron.
These and other advantages of the present invention will become evident to those skilled in the art.
The present invention relates to a microelectromechanical (MEM) apparatus, comprising a substrate; a platform (i.e. a stage) supported above the substrate by a trio of flexible members; and means for bending each flexible member, thereby changing the elevation or tilt of the platform. The substrate generally comprises silicon (e.g. a silicon wafer or portion thereof); and the platform generally comprises monocrystalline or polycrystalline silicon.
Each flexible member is equidistantly spaced about the platform and can be anchored to the substrate directly, or through another element to which the flexible member is connected. The other end of each flexible member can be operated independently of other flexible members supporting the platform thereby enabling the platform to be tilted. Alternately, the flexible members can be operated in unison to elevate the platform above the substrate while maintaining the platform substantially coplanar with the substrate.
The connection of each flexible member to the platform is preferably made using a compliant member. In some embodiments of the present invention, the compliant members connect a point near the midpoint of each flexible member to an outer edge (i.e. the periphery) of the platform. In other embodiments of the present invention, one end of each compliant member is connected proximate to an end of one of the flexible members; and the other end of each compliant member is connected to the platform at a point equidistant from a central axis of the platform (i.e. between the central axis and the outer edge of the platform).
The platform can have an arbitrary shape (e.g. circular or polygonal), and can further be either planar or curved (e.g. with an upper surface curved inward). The platform can also have a mirror coating on a surface thereof (e.g. the upper surface which is also termed herein as the topside) for reflecting an incident light beam. When a mirror coating is provided, the other surface of the platform can include a stress-compensation coating formed thereon, if needed, to compensate for any stress induced in the platform by the mirror coating which might otherwise distort the topography of the platform.
The means for bending each flexible member and thereby elevating or tilting the platform can comprise a microelectromechanical (MEM) actuator (e.g. an electrostatic actuator) which is operatively connected to the flexible member. In some embodiments of the present invention, each electrostatic actuator can comprise an electrostatic comb actuator which further comprises a plurality of stationary electrostatic combs attached to the substrate and a plurality of moveable electrostatic combs attached to a frame supported above the substrate, with the moveable electrostatic combs being moveable towards the stationary electrostatic combs in response to an actuation voltage (i.e. an electrical signal) provided therebetween. Each electrostatic comb further comprises a plurality of spaced fingers, with the fingers of each moveable electrostatic comb being enmeshed with the fingers of an adjacent stationary electrostatic comb.
In other embodiments of the present invention, each electrostatic actuator can comprise a vertical zip actuator which further comprises at least one first electrode supported on the substrate and a second electrode superposed above the first electrode with a spacing between the first and electrodes being variable along the length of the superposed first and second electrodes, and with the second electrode being moveable towards the first electrode in response to an actuation voltage provided therebetween. One end of the second electrode can be connected to the flexible member, and the other end of the second electrode can anchored to the substrate (e.g. through a mechanical latch). In some cases, the vertical zip actuator can be segmented to provide a plurality of separately-connected first electrodes, for example, to allow portions of the vertical zip actuator to be separately addressed for precise and repeatable control of the elevation or tilt of the platform.
In some embodiments of the present invention, each flexible member that is connected to the compliant member can be further connected to a pair of elongate elevation members juxtaposed on both sides of the flexible member, with the elevation members being anchored to the substrate (e.g. through a flexible joint).
To initially elevate the platform above the substrate after fabrication and release thereof, a plurality of pre-stressed members can be provided underneath the platform, with each pre-stressed member being anchored at one end thereof to the substrate, and with the other end of each pre-stressed member providing a force on the platform to urge the platform upward from the substrate. Each pre-stressed member can comprise an oxide material (e.g. silicon dioxide or a silicate glass) encased within a polysilicon body for producing a stress gradient in the pre-stressed member.
A plurality of restraining clips can also be optionally used for holding the platform in place during fabrication thereof, with the restraining clips being moveable away from the platform to release the platform for movement thereof. Alternately, a plurality of fuses (e.g. comprising polycrystalline silicon) can be provided to anchor the platform to the substrate during fabrication thereof, with each fuse being electrically severable to release the platform for movement.
The present invention is also related to a microelectromechanical apparatus comprising a substrate; a platform supported above the substrate by a plurality of flexible members, with each flexible member being connected to the platform at a point between a central axis of the platform and the periphery of the platform; and a plurality of electrostatic actuators providing movement in a direction substantially in the plane of the substrate, with each electrostatic actuator being operatively connected to one of the flexible members to bend the flexible member out of the plane of the substrate, thereby elevating or tilting the platform. A mirror coating can be provided on the platform for reflecting an incident light beam.
Additionally, the present invention relates to a microelectromechanical apparatus comprising a substrate (e.g. comprising silicon); a platform formed on the substrate and having a central axis oriented at an angle (e.g. 90xc2x0) to the plane of the substrate; a plurality of compliant members, each connected at a first end thereof to an underside of the platform (e.g. at a point equidistant from the central axis), with the plurality of compliant members further being arranged symmetrically about the central axis; a plurality of elongate flexible members, each connected at an inner end thereof to a second end of one of the compliant members, with an outer end of each elongate flexible member being operatively connected to an electrostatic actuator; and at least one elongate elevation member connecting each flexible member to the substrate. Each elevation member acts in combination with the flexible member to which the elevation member is connected to elevate or tilt the platform in response to a force provided on the outer end of the flexible member by the electrostatic actuator. Generally, the plurality of flexible members comprises a trio of flexible members.
The platform can be, for example, either circular or polygonal and can include a mirror coating on a topside thereof. If needed, a stress-compensation coating can be deposited on the underside of the platform to compensate for any stress induced in the platform by the mirror coating. The apparatus can further include a plurality of fuses or restraining clips for securing the platform to the substrate, with the fuses being electrically severable and the restraining clips being removable to release the platform for movement.
To aid in elevating the platform, a plurality of pre-stressed members can be located beneath the platform, with each pre-stressed member being anchored at one end thereof to the substrate, and with the other end of each pre-stressed member providing an upward force on the underside of the platform to urge the platform away from the substrate. The pre-stressed members can be elongate, and can be oriented along a line from the central axis. In such arrangement, each pre-stressed member can be anchored to the substrate at a point proximate to the central axis.
The present invention is further related to a microelectromechanical apparatus that comprises a substrate (e.g. comprising silicon); a platform supported above the substrate by a plurality (e.g. two or three) of elongate flexible members; at least one elevation member connected at one end thereof to each flexible member, with the other end of the elevation member being anchored to the substrate through a flexible joint; and an electrostatic actuator operatively connected to the other end of each flexible member to provide a force to the flexible member, thereby flexing the flexible member and elevatating or tilting the platform. The flexible members can be spaced by an angle of 120 degrees (120xc2x0) about a central axis of the platform. Each flexible member preferably supports the platform by a compliant member which connects the flexible member to the platform. For redirecting an incident light beam, the platform can include a mirror coating on a topside thereof. When two flexible members are used, the platform can be anchored on one side thereof to the substrate by a flexible hinge.
Finally, the present invention is related to an apparatus for redirecting an incident light beam that comprises a mirror supported above a substrate for reflecting the incident light; and a trio of electrostatic actuators spaced about a central axis of the mirror and operatively connected to tilt the mirror in response to an actuation voltage provided to at least one of the trio of electrostatic actuators. The substrate can comprise silicon; and the mirror can comprise polycrystalline silicon. The mirror comprises a platform with a light-reflective coating thereon, with the platform being planar to form a planar mirror (i.e. a flat mirror), or with the platform being curved to form a curved mirror (e.g. a spherical mirror).
Each electrostatic actuator can be operatively connected to the mirror through a flexible member which is bendable out of the plane of the substrate. A compliant member can also be located between each flexible member and the mirror to connect each compliant member to the mirror at a point at the periphery of the mirror or between the periphery and the central axis of the mirror. A displacement multiplier can also be located between the electrostatic actuator and the flexible member.